1. Field of the Invention
The invention relates to a camera zoom lens automatic magnification apparatus applied to still cameras and movie cameras which automatically adjusts the focal length of a zoom lens according to the distance to a subject to be photographed and the area coverage of the subject in the angle of field.
2. Description of the Prior Art
When a particular subject is to be photographed continuously, an apparatus such as disclosed in the Japanese Patent Publication No. 1602/1985 can be used which automatically changes the focal length (zoom ratio) of the zoom lens according to the change in the distance to the subject to keep constant the relative size of a subject with respect to the angle of view. The publication also discloses that such an apparatus is very convenient and effective when used in combination with an automatic focusing device.
Another Japanese Patent Publication No. 118328/1987 proposes an apparatus which performs automatic magnification for a two-focal-point camera or a zoom lens camera according to the information on the distance to a subject located at the center in the angle of view.
With the method employed in the above-mentioned apparatuses, the lens magnification control is performed based on only the distance to the subject and the area the subject occupies in the angle of view is not considered at all. As long as the sizes of subjects are uniform, it is possible to make almost constant the relative sizes of subjects with respect to the angle of view by changing the focal length of the zoom lens according to the distance to the subject. However, subjects may be different in size and have different situations and it is very difficult to keep constant the sizes of the subjects relative to the angle of view.
With a conventional distance measuring device, the distance measurement is made of only a small area at the center of the angle of view, so that when the subject is deviated from the central area, the magnification control which is based on the information on distance to the central area will not be performed correctly.